Those compressors commonly used in refrigeration systems of refrigerators in general and in air conditioners should meet some requirements such as reliability, low noise and vibration levels, high energetic yield, small dimensions and low cost. Conventional models on the market only partially meet these requirements.
The pumping of the refrigerant fluid in conventional compressors (of the reciprocating, rotary or centrifugal types, for example) is achieved by the relative movement between some components of these compressors, requiring constant and efficient lubrication for reducing friction and wear between the contacting parts of these components. Although the presence of oil reduces friction and wear in the compressors, it does have some drawbacks, such as the possibility of infiltration in the refrigeration system, the lubricant oil mixing with the refrigerant liquid. The circulation of oil in the refrigeration cycle reduces the efficiency of the system, increasing its energetic consumption. So that the infiltration of oil in the refrigeration system does not contaminate the refrigerant fluid, there should be compatibility between the fluids, which restricts the range of choices of said fluids.
Another drawback of the conventional compressors refers to their energetic consumption to operate the relative movement cited above. A large percentage of energy of said compressors is spent overcoming mechanical friction and inertia and not in pumping the refrigerant gas, thereby limiting the compressor yield and compromising its efficiency. Moreover, the parts with relative movement are continually submitted to mechanical fatigue and wear, requiring more resistant parts, which are consequently more expensive and increase the compressor costs. It has also been observed that the more movable parts a compressor has, higher will be its energetic consumption and costs.
To overcome the above cited problems, solutions have been developed for the pumping system, by pressurizing the refrigerant fluid by thermal variation, stimulating said refrigerant fluid or by the application of sound waves (U.S. Pat. No. 5,020,977, U.S. Pat. No. 5,167,124 and U.S. Pat. No. 5,174,130).
Although other solutions for pumping are known in the state of the art, such as by crystal piezoelectric action (U.S. Pat. No. 5,271,724), such solutions are not applicable to refrigeration systems in general.